The present invention relates to a filter circuit and, more particularly, to a filter circuit composed of a capacitor and a resistor (called hereinafter a "RC filter circuit") incorporated in an integrated circuit device.
A RC filter circuit is used for forming a signal to eliminate a noise component contained therein or converting the wave-form of the signal. The time constant of the RC filter circuit is dependent on the respective values of the capacitor and the resistor. It is, however, unavoidable that the actual values of the capacitor and the resistor deviate from the designed values thereof. In general, each of the capacitor and the resistor has the deviate by 20-30% from the designed value, so that the cut-off frequency of the band pass filter characteristic determined by the time constant of the RC filter circuit often deviates more than 50%. It is therefore required to adjust the time constant of the RC filter circuit. For this purpose, the so-called raiser trimming technique is employed to adjust the value of the resistor and/or the capacitor.
Referring to FIG. 1, the RC filter circuit 100 according to the prior art includes a resistance compensation circuit for adjusting the resistance value of the resistor in the RC filter circuit. Specifically, this circuit 100 includes a resistor series circuit composed of four resistors 16-19 connected in series between an input terminal 101 and an output terminal 102. The circuit 100 further includes a capacitor 20 connected between the output terminal 102 and a ground terminal, and fuses 21-23 connected in parallel to the resistors 16-19, respectively. The resistor 19 has such a resistance value as representing a desired time constant of the circuit 100 when the capacitor 200 has the maximum deviation from the designed value. Each of the resistors 16-18 are thus employed as a compensation resistor. Accordingly, the value of the capacitor 20 is measured by a test equipment, so that zero, one, or more of the fuses 21-23 are blown to adjust the value of the total resistance such that the filter circuit 100 has the desired or intended time constant.
However, in the circuit 100, the test equipment for adjusting the time constant is needed, and adjusting steps are also needed. Moreover, the stress caused by blowing the fuse 21, 22 or 23 is applied to, and may change a semiconductor chip which includes circuit 100.